Fiber optical sensors are optical fiber based sensing apparatuses that have been used for a wide variety of purposes, such as in the areas of energy, medicine, scientific research, industrial applications, etc. Such sensors have outstanding advantages, such as intrinsic safety, corrosion resistance, suitability for remote sensing, and immunity to electromagnetic interference.
Fiber optical sensors used for the detection of target chemicals in a liquid medium having a refractory index of more than 1.33, such as in a water solution, has witnessed a great development in the recent years, yet fiber optical sensors used for the detection of molecules in a gaseous medium having a refractory index of around 1.0, remain to be developed.
In the energy field, for example, hydrogen (H2) is a promising energy source for helping supply the energy demands of the world while reducing toxic emissions from fossil fuels. However, it is also a highly flammable and explosive gas at concentrations ranging from 4%-75% in air, with a low ignition energy and high heat of combustion. Thus, it is vital to have an inexpensive device that can quickly, sensitively, reliably and safely monitor hydrogen concentrations in case there is a leak.
In chemical industry, certain gaseous molecules, such as ammonia (NH3), have served as crucial precursors in the manufacturing of other important chemicals including fertilizers, cleaners, food products, and pharmaceutical products, etc. Yet due to its toxicity, ammonia could cause serious environmental problems if leaked, and thus reliable detection of NH3 gas that has been leaked into the atmosphere is also needed.